Causes of Re-Os Isotopic Variations in High-Temperature Sulfide Mineral Assemblages: Insights From the Duluth Complex-Virginia Formation System

高温硫化物矿物组合中铼锇同位素变化的原因：来自德卢斯杂岩-弗吉尼亚地层系统的见解

• 批准号: 0608645
• 负责人: Edward Ripley
• 金额: $ 24.07万
• 依托单位: Indiana University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-07-01 至 2010-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0608645&HistoricalAwards=false
• 关键词: Causes; Re; Os; Isotopic; Variations

Intellectual Merit: This project will evaluate hypotheses to explain precipitation of sulfide minerals from crustally intruded magmas - that may explain the formation of certain important ore deposits associated with the Duluth intrusive complex. Country rock contamination has been proposed as a requirement to produce sulfide saturation in mantle-derived basaltic magmas, either through assimilation of crustal sulfur, or by assimilation of siliceous material that results in a decrease in the sulfide solubility of the mafic magma. The Re-Os isotopic system has proven particularly useful in evaluating the role of crustal contamination in magmatic ore deposits and in mantle-derived rocks in general. Because of the chalcophile nature of both Re and Os, the system is well-suited as an indicator of crustally derived metals in sulfide mineralization. However, recent studies have shown that the Re-Os isotopic system may be particularly prone to perturbations related to later interaction with fluids. Previous S isotopic studies of likely country rock contaminants suggest that these rocks were the principal source of sulfur for the magmatic sulfide mineralization associated with the Duluth complex. However, preliminary Re-Os isotopic studies indicate that sulfide minerals in the contact aureole are characterized by unradiogenic Os whereas the massive sulfide mineralization at Duluth is characterized by radiogenic Os - indicative of extensive Os contamination. Extreme Re-Os isotopic variations in the sulfide systems in these rocks are reflective of fundamental processes that must accompany the interaction of mafic magmas with crustal rocks. Veins in the contact aureole contain quartz and a sulfide assemblage (pyrrhotitecubainte-pentlandite) that is very similar to that found in the magmatic sulfide mineralization. In order to test the premise that the perturbation of the Re/Os isotopic system in the contact aureole is related to the reaction between Re-Os-bearing fluids and sulfide minerals, fluid inclusion, stable isotopic, and Re-Os isotopic studies of the vein material, as well as spatially associated sedimentary sulfides, are planned. These data will allow assessment of the origin and composition of the fluid, and its relationship to the magmas of the Duluth Complex. Because large xenoliths of country rocks that preserve low-grade mineral assemblages in their cores are present in the intrusive rocks of the Complex, we will also be able to systematically evaluate the mechanisms responsible for Re-Os and S isotopic variations from xenolith cores through metamorphosed margins and surrounding disseminated sulfide-bearing igneous rocks. The results of this study will shed light on the causes of Re-Os isotopic variations in sulfide systems related to mafic magma-crust interaction, and will be of particular value in the evaluation of Re-Os isotopic systematics associated with magmatic sulfide ore formation.Broader Impacts: Broader aspects of the proposed research include the training of both graduate and undergraduate students in systematic field sampling and in the use of state-of-theart analytical facilities for chemical and isotopic analyses at three NSF-funded laboratories. Cooperation with the Minnesota Natural Resources Research Institute will be essential for the project to succeed. Exploration for, and utilization of, metallic resources found in magmatic systems continues to grow as third-world economies strengthen. Knowledge of how an often utilized radiogenic isotopic system may respond to high-temperature events involving magmas and fluids is essential to the development of future exploration models.

智力价值：该项目将评估解释地壳侵入岩浆中硫化物矿物沉淀的假设，这可能解释与德卢斯侵入杂岩相关的某些重要矿床的形成。围岩污染被认为是在地幔玄武岩岩浆中产生硫化物饱和的一个要求，或者通过地壳硫的同化，或者通过硅质材料的同化，导致镁铁质岩浆的硫化物溶解度降低。事实证明，Re-Os 同位素系统对于评估岩浆矿床和地幔衍生岩石中​​地壳污染的作用特别有用。由于铼和锇均具有亲铜性质，该系统非常适合作为硫化物矿化中地壳衍生金属的指示剂。然而，最近的研究表明，Re-Os 同位素系统可能特别容易受到与随后与流体相互作用相关的扰动。先前对可能的围岩污染物的硫同位素研究表明，这些岩石是与德卢斯杂岩相关的岩浆硫化物矿化的主要硫来源。 然而，初步的铼-锇同位素研究表明，接触光环中的硫化物矿物的特征是非放射性锇，而德卢斯的块状硫化物矿化体的特征是放射性锇，这表明存在广泛的锇污染。这些岩石中硫化物系统的极端铼锇同位素变化反映了镁铁质岩浆与地壳岩石相互作用所必须伴随的基本过程。接触光环中的矿脉含有石英和硫化物组合（磁黄铁矿-镍黄铁矿），该组合与岩浆硫化物矿化中发现的非常相似。为了检验接触光环中Re/Os同位素系统的扰动与含Re-Os流体与硫化物矿物之间的反应有关的前提，对流体包裹体、稳定同位素以及Re-Os同位素进行了研究。脉状物质以及空间相关的沉积硫化物均已规划。这些数据将有助于评估流体的来源和成分，及其与德卢斯杂岩岩浆的关系。由于杂岩体的侵入岩中存在大型围岩捕虏体，其核心保留了低品位矿物组合，因此我们还能够系统地评估通过变质作用导致捕虏体核心 Re-Os 和 S 同位素变化的机制。边缘和周围浸染状含硫化物火成岩。本研究结果将揭示与镁铁质岩浆-地壳相互作用相关的硫化物系统中Re-Os同位素变化的原因，对于评价与岩浆硫化物矿形成相关的Re-Os同位素系统具有特殊价值。更广泛的影响：拟议研究的更广泛方面包括对研究生和本科生进行系统现场采样培训以及使用最先进的分析设施进行化学和同位素分析。三个 NSF 资助的实验室。与明尼苏达自然资源研究所的合作对于该项目的成功至关重要。随着第三世界经济的增强，对岩浆系统中金属资源的勘探和利用不断增长。了解经常使用的放射性同位素系统如何响应涉及岩浆和流体的高温事件对于未来勘探模型的发展至关重要。